When we switched to a new product model, we found that the same Jia Jinyuan soldering auxiliary material performed well with no-clean process on Customer A's production line, but frequently caused ICT test floating height issues on Customer B's production line. We later identified the root cause: Customer B strictly controls ion residue within 0.1μg/NaCl/cm2, while Customer A only requires compliance with L0 level activity per IPC-J-STD-004B. Therefore, process decisions cannot be made solely based on model labels; it is necessary to comprehensively determine whether to enable no-clean mode by combining customer inspection standards, post-reflow board residue morphology, cleaning equipment water pressure, and DI water conductivity.

The rosin content of Jia Jinyuan's no-clean soldering auxiliary material is controlled at 2.8%±0.3%. Combined with low-boiling-point alcohol ether solvents, over 95% of Flux residues carbonize into a transparent thin layer at the 230℃ peak reflow temperature. This design ensures that PCBA after SMT placement feels non-sticky and has no obvious reflection at room temperature. However, if the customer plans to apply conformal coating later, it is necessary to verify whether the adhesion attenuation between this carbonized film and polyurethane coating exceeds 15%. We once reworked 2700 pieces on an LED driver board project due to this issue.

Water-washable Soldering Auxiliary Materials reduce the rosin ratio to below 1.2% and add a specific proportion of organic acid salt complexing agent, enabling complete dissolution within 6 seconds under 50℃ pure water spraying. However, note that the conveyor speed of the water washing machine must match the flux residue thickness. When the Solder Paste printing thickness exceeds 150μm, even extending the spraying time to 9 seconds will still form water stain rings at the bottom of QFN packages. In this case, the solder paste supplier must be required to adjust the thixotropic index from 4.2 to 4.8 to improve slump control.

We compared three states under the same reflow profile: after reflow in a nitrogen atmosphere, the surface insulation resistance of no-clean material exceeds 10^10Ω; after DI water rinsing and drying, the ion chromatography test of water-washable material shows a Cl? concentration of 0.03μg/cm2; however, when no-clean material is mistakenly run through the water washing line, slight fluctuations in spray pressure will cause white crystal precipitation at the edge of 0402 component pads. These crystals accelerate the segregation and growth of intermetallic compounds (IMC) after -40℃ thermal shock testing.

The technical parameter sheet provided by Jia Jinyuan clearly marks the SIR test conditions for each soldering auxiliary material. However, on-site engineers cannot only focus on the 7-day/85℃/85%RH data; they must also pay attention to the insulation resistance attenuation slope after 1000 hours of high-temperature storage at 125℃. This is because failures in automotive MCU modules often do not originate from humid environments, but from sudden leakage current increases after long-term high-temperature aging. In such cases, the resin crosslink density of no-clean material is at least 23% higher than that of water-washable material.

The biggest concern during production line changeover is mistakenly loading water-washable soldering auxiliary material into a no-clean solder paste can. Although both have a viscosity around 750Pa·s, the former will show obvious solvent stratification after staying at the stencil aperture for 30 seconds, leading to a first-piece Printing Solder Paste volume deviation of ±18%. The latter, due to the addition of thixotropic reinforcing particles, can maintain printing consistency even after a 15-minute downtime. This difference directly determines whether the open-circuit defect rate is 0.012% or 0.27% on 0.3mm pitch BGA packages.